It has been known in cross-country skis to provide the running surface in the central longitudinal region with a scale-like structure so as to obtain a sawtooth-shaped extension with a multiplicity of scales whose backs rise gently towards the rear end of the ski and are defined by steep faces, the array of which provides an increased sliding resistance when the ski moves oppositely to the running direction. However, regardless of the shape and the distribution of the scales, an increased sliding resistance in the running direction also has to be accepted with running surfaces having such a structure.
For increasing the climbing aid achievable with a scale-like structure of the running surface, it has been known (German Laid-Open Patent Application No. 27 23 176) to design the scales in the form of teeth or tongues having ends which are capable of being bent upwards so that upon back-sliding of the ski the sliding resistance is increased by upward bending of the teeth or tongues. It is a drawback of such a construction that the teeth or tongues have a considerable bending resistance and accordingly the desired effect is not always achieved. When providing the end portions of the tongues or teeth with pointed ends which are directed towards the end of the ski and are capable of being bent upwards (French Pat. No. 22 69 358), the bending resistance of the pointed ends capable of being bent upwards may be reduced considerably because it is not the teeth or tongues themselves that must be bent upwards, however, the production of such teeth is expensive. Besides, the sliding resistance in the running direction is relatively high.
For reducing the sliding resistance in the running direction, it has been known (German Laid-Open Patent Application No. 26 10 522) to profile the running surface by milling grooves extending transversely to the longitudinal direction of the ski, wherein the milled grooves may be applied crosswise. With such milled grooves, which have only a small depth, the sliding resistance in the running direction may be improved relative to conventional scale-type skis. However, this improvement is attained at the expense of the effectiveness of the climbing aid so that such running surface structures have not been successful in practice.
Mention may be made of the aforementioned application which describes forming the running surface with a multiplicity of teeth defined by two families of parallel running surface cuts intersecting each other in the running surface, the individual families of cuts being inclined to a normal of the running surface in opposite directions. Since the running-surface cuts start from the plane running surface, the tooth backs are in the running surface, whereby improved sliding properties are ensured.
While this arrangement has proved to be a major advance in the art as noted below, and the present invention extends principles thereof, nevertheless there is a high sliding resistance when the ski is moved oppositely to the running direction because the pointed ends of the teeth are bent out of the plane of the running surface when the ski slides backwards and are again urged back into the plane of the running surface upon subsequent forward sliding movement. Since by means of the direction and size of the running-surface cuts tooth shapes with different effects may be produced in a simple way, it is possible to match the running-surface coatings to most varied conditions. Although such running surfaces have been successful in practice, it is desirable to meet different requirements with a single running-surface configuration instead of providing different running-surface shapes for different uses of the ski.